Dancer, possibly, almost certainly stops concerning Rambert's principal (8)
I believe the answer is:
reindeer
'dancer possibly' is the definition.
(Dancer is one of Santa's reindeer)
'almost certainly stops concerning rambert's principal' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'certainly' becomes 'indeed' (I've seen this before).
'stops' indicates putting letters inside.
'concerning' becomes 're'.
'rambert's principal' becomes 'r' (I can't justify this - if you can you should believe this answer much more).
'indeed' with its last letter taken off is 'indee'.
're'+'r'='rer'
'indee' placed inside 'rer' is 'REINDEER'.
(Other definitions for reindeer that I've seen before include "Large animal of northern regions" , "Santa's sleigh pullers" , "Antlered animal" , "Dancer, Prancer etc." , "'Dancer or Prancer, say (8)'" .)